New cytochemical methods for identification of various types of hemopoietic cells were developed. Marrow cells were stained successively for the enzymatic activities of chloroacetate esterase (red color) and myeloperoxidase (yellow color) and afterwards counterstrained with methyl green (green color). Various color combinations appear in the cytoplasm of different types of hemopoietic cells, which made cell differentiation much easier than the standard methods. Growth of megakaryocytes was succeeded in cultures of bone marrow cells. A 10-fold increase in the number of megakaryocytes was observed in a period of 5-6 days. The membrane demarcation system and the platelet liberation phenomenon were clearly shown.